Over the years, a variety of implantable electrochemical sensors have been developed for detecting and/or quantifying specific agents or compositions in a patient's blood. For instance, glucose sensors have been developed for use in obtaining an indication of blood glucose levels in a diabetic patient. Such readings are useful in monitoring and/or adjusting a treatment regimen which typically includes the regular administration of insulin to the patient. Thus, blood glucose readings improve medical therapies with semi-automated medication infusion pumps of the external type, as generally described in U.S. Pat. Nos. 4,562,751; 4,678,408; and 4,685,903; or automated implantable medication infusion pumps, as generally described in U.S. Pat. No. 4,573,994, which are herein incorporated by reference.
Generally, small and flexible electrochemical sensors can be used to obtain periodic readings over an extended period of time. In one form, flexible subcutaneous sensors are constructed in accordance with thin film mask techniques in which an elongated sensor includes thin film conductive elements encased between flexible insulative layers of polyimide sheets or similar material. Such thin film sensors typically include a plurality of exposed electrodes at one end for subcutaneous placement with a user's interstitial fluid, blood, or the like, and a corresponding exposed plurality of conductive contacts at another end for convenient external electrical connection with a suitable monitoring device through a wire or cable. Typical thin film sensors are described in commonly assigned U.S. Pat. Nos. 5,390,671; 5,391,250; 5,482,473; and 5,586,553 which are incorporated by reference herein. See also U.S. Pat. No. 5,299,571.
Drawbacks to the use of implantable sensors arise from the use of a wired connection between the implantable sensor set and the monitor. The use of the wire or cable is an additional inconvenience to users that already utilize an external infusion pump that includes an infusion insertion set and tube to infuse the medication. Also, the preferred site for some sensing device may be inconvenient for connection by wire to a characteristic monitor. For implantable pumps, the wire or cable negates the very benefit of having an internal device without external wires or cables. For Type 2 diabetics, who do not necessarily need or use an infusion pump, the use of a cable is seen as an inconvenience that may inhibit use of the device. In addition, the use of a wire or cable limits a user's ability to position the monitor, since it can be placed no further away than the ultimate length of the wire or cable. Thus, the user must normally wear the monitor, which can be problematic. For example, removal of the monitor for sleeping can be difficult, since a user would tend to become “tangled” in the wire or cable, between the sensor and the monitor, during the normal tossing and turning that occurs during sleep. Furthermore, the more connections the user must deal with (e.g., infusion pump and catheter and/or monitor with wire to sensor), the more complicated it is to use the devices, and the less likely the user will maintain compliance with the medical regimen due to perceived and actual difficulties with all of the wires and cables.